Exploring the Enhancement of Photocatalytic Performance in TiO₂ based Hollow Composites: Size Effect of the Adsorbed CeO₂ Particles

Abstract The photocatalytic (PC) behavior of CeO 2 –TiO 2 hollow composites with different heterojunction structures are investigated. The composites are fabricated by combining TiO 2 hollow spheres and CeO 2 nanoparticles with changing the ratio between Ce and Ti. High‐resolution microscopic and spectroscopic analysis demonstrates that three types of cerium‐bearing structures form on the surface of the titania. The first involves Ce atoms adsorbed onto the surface of TiO 2 particles. The second occurs with small CeO 2 particles, ≈2 nm in size, resulting from the aggregation of the adsorbed Ce atoms, thus forming a CeO 2 –TiO 2 heterojunction. The last type is obtained through the growth of the CeO 2 particles up to 10 nm in size. All the CeO 2 –TiO 2 composites exhibit enhanced photocatalytic degradation of methyl orange under visible light irradiation compared to mere CeO 2 or TiO 2 nanoparticles. The synergistic effect of these three structures leads to a competition between size effects and interface interactions, which affects the band alignment, the number of defects, and, consequently, the PC activity. The highest PC reaction rate constant under visible light reaches up to 0.017 min −1 and is achieved when the CeO 2 nanoparticle size is smaller than its Debye length.